Researchers at the University of California, Los Angeles (UCLA) have discovered a chemical reaction that seems to effectively convert highly stable alkanes into more valuable compounds. Non-classical carbocations — ions with fewer electrons than protons, and thus a positive charge — contributed to the surprising results. The reaction, the researchers say, someday might play a role in turning petroleum waste into feedstocks for pharmaceuticals or even pharmaceuticals themselves.
Figure 1. The research team includes, from left, Stasik Popov, Alex Bagdasarian, Hosea Nelson and Brian Shao. Source: Penny Jennings/UCLA Chemistry & Biochemistry.
“Alkane functionalization is usually performed using heterogeneous catalysts or expensive transition metals. Here, we use catalysts composed of silicon and boron, and the chemistry occurs through an unusual mechanism. While it is far from perfect, it seems that this approach may be complementary to these other approaches,” explains Hosea Nelson, a UCLA assistant professor of chemistry and biochemistry.
To better understand the process, the researchers conducted further research using molecular dynamics simulations and found the reaction involves formation of a non-classical carbocation.
The researchers discovered that because the charge is shared among multiple atoms — the non-classical model — the molecule has more flexibility to undergo a diverse array of reactions, including those needed to break apart the strong bonds of alkanes.
“This was a surprising fundamental finding,” Nelson says. “It introduces a lot of other questions, and we think that the non-classicality of these reactions will allow us to break a lot of the rules of chemical synthesis to develop new types of reactions.”
The findings, the researchers say in an article published in Science, lay the conceptual and experimental groundwork for further discoveries in the field of alkane C–H bond functionalization using ketone derivatives and weakly coordinating anion (WCA) catalysis.
“We have developed a whole new way to think about reactions through our molecular dynamics simulations,” adds Kendall Houk, a professor who worked on the project.
Nelson suspects the reaction could even break apart the long alkane molecules found in some non-biodegradable plastics. His group is pursuing both applications in more detail.
“We are trying to use this chemical reaction to use methane and other light hydrocarbons as building blocks for complex molecule synthesis and to convert polyethylene into new polymers with different properties,” notes Nelson.
Further work also will involve developing cheaper precursors and simpler catalysts that will allow use of these chemistries in a broad range of practical applications. “The overall process may take ten years, but we will be publishing some advances in the coming months,” he says.
“This is far from perfect, and really reserved for academic study at this point. We have a long way to go until industrial chemists use reactions like this,” Nelson cautions.